1. Field of the Invention
The present invention relates to an optical system comprising a fiber-optic amplifier including a section of optical waveguide doped with a rare-earth element and a pump-light source emitting pump light, which converts signal light of a first wavelength which is to be transmitted to signal light of a second wavelength, and including an optical-to-electrical transducer for receiving the signal light of the second wavelength.
The invention also relates to the use of the fiber-optic amplifier.
2. Background Information
The term "optical system" as used herein means a combination of different optical devices, such as lasers and fiber-optic amplifiers, which interact and may be spaced far apart.
Fiber-optic amplifiers are commonly used to amplify the optical signal guided in an optical waveguide. Optical systems of the above kind are known. Hence, the use of the fiber-optic amplifiers contained therein is also known.
U.S. Pat No. 5,247,529 (corresponding to EP-A2-0514686) discloses an optical system which shows a further possible use of a fiber-optic amplifier (FIG. 4). The fiber-optic amplifier contained in that system is shown in its usual manner of representation, with a doped section of optical waveguide and a pump-light source. The doped section of optical waveguide is fed with modulated light having a wavelength of 850 nm from at least one transmit laser. It is also fed with unmodulated light, which can be amplified in the fiber-optic amplifier. This light has a wavelength of 1550 nm. The fiber-optic amplifier outputs modulated light with a wavelength of 1550 nm.
In that system, the wavelength of the light to be transmitted is fixed at 1550 nm, since at this wavelength the optical waveguides have an attenuation minimum. On the other hand, the use of light of this wavelength, which represents the optimum wavelength in terms of attenuation, involves increased complexity at the transmitting and receiving ends; specific transmit lasers and photodiodes have to be employed.
In the prior art system, the problem that specific transmit lasers have to be used is solved by employing, instead of an expensive laser which emits light at a wavelength of 1550 nm, a low-cost laser which emits light at a wavelength of 850 nm, and converting the signal light with a wavelength of 850 nm to signal light with a wavelength of 1550 nm.
No possibility of avoiding the use of expensive photodiodes suitable for receiving light with a wavelength of 1550 nm is indicated.